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Transcript of GaAs
Gallium ArsenideGaAs
By:Nhi Mai, Ricardo Lopez, Eric Leal,
Hector Leal Brol, James Lillian
ENGR2300 – Materials EngineeringNovember 2011
Outline Introduction History Properties Manufacturing Processes Cost Applications Conclusion
Introduction
Gallium Arsenide (GaAs) is a combination of one gallium atom (atomic no. 31) and one arsenic atom (atomic no. 33). The atoms are arranged in a cubic sphalerite lattice. It has a FCC symmetry. The unit cell contains four GaAs molecules. Gallium atoms bond to four arsenic and each arsenic atom bonds to 4 gallium atoms.
Gallium Arsenide
Elemental Gallium does not occur naturally in nature but in trace amounts with bauxite and zinc. It is a byproduct during those ores’ processing. In its pure form gallium is a soft, brittle and silvery metallic in color. Elemental gallium melts slightly above room temperature and will melt in your hand.
Introduction Gallium
Introduction Arsenide
Arsenic is a highly toxic element that is found with many minerals, especially sulfur, and can be found naturally as a pure substance. Its main industrial use is as a strengthener in alloys with copper and lead. Arsenic is also in declining use in pesticides and herbicides.
History Dmitri Mendeleev
predicted all elements’ properties on the periodic table
1875, Lecoq de Boibaudran discovered Gallium in the Pyrenees Mountains
Method to retrieve Gallium: electrolysis
Gallium
History Arsenic
Been known since the Bronze Age
1250, discovered by Albert the Great
Used as an impurity in bronze
Later found that Arsenic was poisonous
Has symptoms that were difficult to distinguish
History Gallium Arsenide
Discovered by Victor Goldschmidt
First to combine these elements
1954, produced a large amount for research on use of this compound
Since 1960s, used in many devices such as solar cells, light-emitting diodes, lasers, and optoelectronic devices
Properties & Crystal Structure
Gallium, a poor metal, has atomic number 31 and it is located in group 13, period 4, and block “p”. Its mas is 69.72 amu, and has no electronegativity according to Pauling.
Arsenic, a metalloid, has atomic number 33 and it is located in group 15, period 4, and block “p”. Its mas is 74.92 amu, and has an electronegativity of 2.18 according to Pauling.
Electrical &Thermal Properties Electrical Properties
Band gap (eV) = 1.42 Electrical conductivity
1X10-6 (Ω*m)-1 Electron mobility 7.7 m2 /
V*s Hole mobility .07 m2 / V*s Electron thermal velocity
4.4X105 m/s Hole thermal velocity
1.8X105 m/s
Thermal Properties
GaAs has a thermal conductivity of 0.55 W/cm-C
Melting point 1238 °C Specific heat 0.33 J g-1°C -1
Thermal diffusivity 0.31 cm2s-1
Thermal expansion, linear 5.73X10-6 °C -1
Crystal StructureThe GaAs crystal is
composed of two sublattices.
Each sublattice are face centered cubic (fcc) lattice.
They offset with respect to each other by half the diagonal of the fcc cube.
This crystal configuration is known as cubic sphalerite or zinc blende.
GaAs has basically outdone silicon in every imaginable way due to its incredible characteristics.
These characteristics make GaAs and ideal candidate for use in mobile phones, satellite communications, microwave point-to-point links, and some radar systems.
GaAs Properties (Room
Temperature)
GaAs vs. SiliconGaAs
Higher saturated electron velocity and higher electron mobility.
GaAs devices generate less noise than silicon and have higher breakdown voltages.
It has a direct bandgap which means that it can be used to emit light.
Silicon Considerably cheaper
than GaAs Existence of silicon
dioxide (one of the best known insulators of any kind)
Posses a much higher hole mobility which allows for the construction of higher-speed P-channel field effect transistors.
Manufacturing Process Ignot
Growing Ingot is a mold or cast of
a substance in bulk quantity ex: gold bars
Ingots can be grown 2 ways: Bridgman Method, or Czochralski Method
CM: Molten GaAs is slowly pulled upwards with a seed crystal while cooling
BM: melting pure GaAs and cooling it from one side. No pulling.
Centromax.net
Manufacturing Process Wafer
Processing GaAs wafers are cut
from ingots. Requires mechanical
and chemical steps such as etching, cropping, thermal treatment and polishing.
Single crystal wafers are then used for another process, Epitaxy.
Manufacturing Process Epitaxy
Epitaxy- gowing a thin single crystal layer over a single crystal substrate
Molecular Beam Epitaxy (MBE)
Molecular beams sending molecules to the substrate through a vacuum, substrate is heated exciting molecules eventually sticking to substrate
Metal Organic Vapor Chemical Deposition (MOVCD)
Similar to MBE except layer is formed by chemical reactions rather than physical placement
CostExpensiveGallium is rareAttempts to lower cost
by recycling substrates or using cheaper substrates such as germanium or silicon
Silicon max efficiency 25%
GaAs efficiency 30%
Applications
Limit cost Improve integrated circuits in all aspects of technologies.
Due to its unique qualities, GaAs can be used in computers, lasers, solar cells, aerospace technology, medical devices etc.
Applications Solar Cells
Solar panels consist of photovoltaic solar cells Leading focus in respect to applying it to solar
cellsUsed in photovoltaic solar cells for numerous
reasons: – GaAs has a high absorption rate – Very thin– Records for highest efficiency (25%)
Has a direct band gap, because of efficiency rate, leads to shrinking of solar cell sizes thus reduction in area
Photovoltaic applications include:– Satellites, cars, calculators highway signs
Applications Aerospace Projects such as the Rovers Spirit and
opportunity, which are exploring Mars’ surface, have used GaAs for its solar cell power source
Radiation hardness. “Single effect events,” (SEEs) associated with the transit of heavy ions through semiconductor junctions have to be minimized to reduce failure risk. Radiation effects from particles can cause degradation, and also failure of the electronic systems in space vehicles or satellites
GaAs has promising future aerospace applications in satellites, space crafts, signal devices, sensors
Applications Transistors
Having a higher electron mobility, this allows flow of electricity in transistors to flow much faster and can lead to many future applications such as: – faster computers– better wireless communication devices
Faster response times for transistors from GaAs
Less propagation delay, less noise to date using molecular beam epitaxial GaAs FETs
Applications
GaAs power amplifiers operate at higher power levels, have higher linearity and sharper edges, can be operated at higher power levels because they have higher breakdown voltages and allow maximum channels to be used
More efficient solar cells GaAs technologies allows to design at lower
frequencies, with less power consumption, over a smaller area, providing a size and power advantage to multi-function integrated solutions for circuits and many more technologies
Conclusion Cost expensive, but hopefully will decrease over
the years GaAs has excellent electronic properties.
(It is superior to Silicon.) Powerful in the electronic industry:
Aerospace Transistors Solar Cells